This invention relates to a relay valve for an air brake system which automatically controls the brake actuator pressure in accordance with the payload of the vehicle equipped with such system.
Wheels of heavy duty vehicles, such as buses, trucks, and trailers, are subjected to wide load variations depending on whether the vehicles are laden or not. Also, the ratio of the load components the front and rear wheels must bear varies sharply on braking and deceleration. For these vehicles it is necessary that adequate distribution of the braking force among the wheels be attained to avoid premature locking of some wheels and ensure the safety of the vehicles when the brake is applied.
Usually the safety of the vehicles at the time of braking has been secured in the following manner. In a conventional air brake circuit as schematically shown in FIG. 1, a brake valve a gives an indicated pressure to actuate a relay valve b, so that air under pressure from an air reservoir c is supplied to a brake actuator d. Vehicles using a service brake circuit of this type are equipped with pressure-regulating means in the form of a load-sensing proportion valve e installed between the brake valve a and the relay valve b. The valve e senses the payload on the vehicle in terms of the distance between the upper and lower end surfaces of the suspension, regulates the indicated pressure from the brake valve on the basis of the value so sensed, and then transmits the regulated pressure to the relay valve.